MOLECULAR SYSTEMATICS AND RADIATION OF THE HAPLOCHROMINE CICHLIDS (TELEOSTEI, PERCIFORMES) OF LAKE MALAWI

Mitochondrial DNA (mtDNA) restriction fragment length polymorphisms we re assayed among 40 species of Lake Malawi haplochromines (Cichlidae) including representatives of ecologically divergent genera. Six distin ctive mtDNA lineages were distinguished, two of which were major clade s, represented by a large number of species. The other four lineages w ere each represented by a single species with a divergent mtDNA haplot ype. One of the two major clades was composed of the shallow-water, ro ck-dwelling mbuna species, whereas the other included a diverse array of sand-dwelling and pelagic species. A number of taxa, found to be fi rmly embedded within the mbuna clade, are quite distinct in morphology and generally inhabit deeper, sediment-rich areas rather than the roc ky habitats typical of other mbuna. The mbuna group is generally thoug ht to be a monophyletic assemblage, but these results suggest that it is actually paraphyletic. In contrast to the high morphological divers ity among Malawi haplochromine species, mtDNA sequence divergence was found to be remarkably low. This finding underscores the unprecedented rapidity of speciation and evolutionary plasticity in this fish speci es flock.